MONTPELIER — A Vermont House committee is soon expected to finish a gasoline tax increase that would take effect over the next two years.

The House Transportation Committee is expected to approve a 2 percent sales tax on gasoline that would take effect in June. In July of 2014, the sales tax would go up another 2 cents on a dollar, to 4 percent.

Meanwhile, in fiscal 2015, the cents-per-gallon tax would drop by nearly 6 cents from its current level of 19 cents per gallon. The upshot would be nearly $26 million more in gasoline taxes collected by the state.

Lawmakers have been looking for ways to shore up transportation revenues. Declining sales of gasoline have cut into revenues from gasoline taxes that historically have been raised mainly on a per-gallon basis.